F-string debug mode does not print correctly when in last line of file #105831
Description
Where there's an f-string that has a debug expression in the last line of a file, the debug expression buffer is one character too short. For example:
```python3
cpython on ξ main via C v14.0.3-clang via π pyenv 3.11.3 took 15s
β― cat tmp/t.py
print(f'''{
3
=}''')%
cpython on ξ main via C v14.0.3-clang via π pyenv 3.11.3
β― ./python.exe tmp/t.py
3
3A fix is already up as part of gh-105828, so just opening this to track the issue.